The invention relates to an apparatus on a spinning preparation machine, especially a flat card, roller card or the like, for adjusting the carding clearance.
It is known for a clothed roller, for example a cylinder, to have a cylindrical peripheral surface facing and spaced radially from a cladding, wherein between the peripheral surface of the roller and a part of the cladding there is a carding region with a carding clearance between clothings facing each other where carding work is performed and carding heat is generated, and in which heat leads to an alteration across the width of the machine in the contour of at least one of the components facing each other.
The distances between the cylinder clothing and surfaces (countersurfaces) facing them are of considerable importance in respect of engineering and fibre technology. The carding result, namely, degree of cleaning, nep formation and fibre shortening, is substantially dependent on the carding gap, that is, the clearance between the cylinder clothing and the clothings of the revolving and stationary flats. The air flow around the cylinder and the dissipation of heat are likewise dependent on the clearance between the cylinder clothing and facing clothed or also unclothed surfaces, for example, separation blades or cover elements. The clearances are subject to different, in some cases counteracting, influences. The wearing down of clothings facing each other results in an enlargement of the carding gap, which is associated with an increase in the number of neps and a reduction in fibre shortening. An increase in the speed of revolution of the cylinder, e.g. to enhance the cleaning action, results in an expansion of the cylinder inclusive of the clothing owing to the centrifugal force, and hence in a reduction in the carding gap. The cylinder expands also when processing large quantities of fibre and certain types of fibres, e.g. synthetic fibres, owing to a temperature increase that is greater than in the remainder of the machine surrounding the cylinder, so that the clearances also decrease for that reason. The machine elements lying radially opposite the cylinder, for example, stationary carding segments and/or separation blades, also expand.
The carding gap is influenced particularly by the machine settings on the one hand and the condition of the clothing on the other hand. The most important carding gap of a revolving flat card is located in the main carding zone, i.e. between the cylinder and the revolving flat assembly. At least one clothing, which delimits the operating clearance of the carding zone generally, is in motion. In order to increase the output of the card, efforts are made to select the operating speed of rotation and the operating speed of the moving elements as high as the technology of fibre processing will allow. The operating clearance is located in the radial direction (starting from the axis of rotation) of the cylinder.
In carding, ever larger amounts of fibre material are being processed per unit of time, which involves higher speeds of the work elements and higher installed capacities. With the work surface remaining constant, increasing throughput of fibre material (output) leads to greater generation of heat owing to the mechanical work. At the same time, however, the technological carding result (sliver uniformity, degree of cleaning, reduction of neps etc.) is continually being improved, which requires more active surfaces engaged in carding, and settings of these active surfaces closer to the cylinder (drum). The proportion of synthetic fibres to be processed is continually increasing, with more heat, compared with cotton, being produced as a result of friction from contact with the active surfaces of the machine. The work elements of high-performance cards are today fully enclosed all round in order to comply with the high safety standards, prevent particle emission into the spinning works environment and minimise the need for maintenance of the machines. Gratings or even open, material-guiding surfaces that allow exchange of air belong to the past. The circumstances described appreciably increase the input of heat into the machine, whereas there is a marked decrease in the discharge of heat by means of convection. The resulting increased heating of high-performance cards leads to greater thermoelastic deformations, which have an influence on the set spacings of the active surfaces owing to the uneven distribution of the temperature field: the distances between cylinder and card top, doffer, fixed card tops and separation points with blades decrease. In an extreme case, the gap set between the active surfaces can close up completely as a result of thermal expansion, so that components moving relative to one another collide. The high-performance card concerned then suffers considerable damage. Moreover, in particular the generation of heat in the working region of the card can lead to different thermal expansions when the temperature differences between components are too large.
To reduce or avoid the risk of collisions, in practical operation the carding gap between clothings facing each other is set to be relatively wide, i.e. a certain safety clearance exists. A large carding gap, however, leads to undesirable nep formation in the card sliver. In contrast, an optimum, especially narrow size is desirable, whereby the nep count in the card sliver is substantially reduced. Displacement relative to one another of the elements facing each other leads to a change in the clearance (carding gap) across the overall width of the machine.
The carding gap has a significant influence on the carding result. That is to say, a carding gap that is as uniformly narrow as possible across the working width produces optimum results. For the cylinder, it follows from this that the integrity of its cylindrical shape is of crucial importance. With reference to the cylinder, there is a further problem in that it is unevenly heated across the working width as a result of varying material coverage and fluctuations in the gap as a consequence of manufacturing tolerances. In addition, heat is dissipated more at the edge regions than in the middle, so that heat accumulates in the middle. This leads to a temperature gradient from the middle of the working width to the edges. The different thermal expansion brought about by this causes a convexly shaped bulging (camber) of the cylinder and thus impairs the carding gap. The carding result is consequently adversely affected. Since the cylinder is a counterpart for all carding and separation points, this loss of quality occurs at all points. In the case of the elements facing each other, e.g. the cylinder and carding elements, generation of heat during operation causes a marked expansion in the middle that reduces towards the edge regions. The disadvantage is that the carding gap is thus uneven across the width of the card and in the middle region there is a risk of collision between the components.
In a known apparatus (WO 2004/106602 A), in the case of a roller and a work element that face each other at least one contour is made concave (hollow) in the course of manufacture. The extent of the hollow machining corresponds to the expected thermal expansion during an intended output. The correction is designed for an ideal output amount. In particular, allowances are made for the expected expansions such that no re-adjustment of the spacing of the individual components with respect to one another is needed. One disadvantage is that presetting of a specific concave contour allows only a single alteration in the curved shape of the elements during operation. Adaptation to changed processing conditions, especially a change in the fibre material volume and quality, is therefore not possible. In addition, it is inconvenient that the inherent heat of the elements in operation, which causes the expansions, is constant, so that the curved form is correspondingly constant and cannot be adapted to changed production conditions.